Polymers and other plastics have been developed which are useful in many applications including automotive parts, engineering plastics, toys, containers, molded items and packaging films. It is often desirable to decorate or to protect items made from these plastics by applying a coating or an aesthetically pleasing design to the plastic. It is obviously important that the coating is tightly bonded to the plastic surface. Plastic surfaces as well as certain non-plastic surfaces such as metal including aluminum and galvanized steel are not particularly receptive to the application of adherent coatings because the surfaces are essentially non-porous. Accordingly, there is a continuing need for coating compositions which exhibit excellent adhesion to plastics and metals, and in particular, to plastics.
Improved adhesion of decorative and protective coating compositions to various substrates, and in particular, non-porous substrates, has been achieved by the application of base coats or primer coats to the substrate prior to the application of the desired decorative coating. Since primer coatings are not visible, they do not have to possess all of the desirable characteristics of the top coatings such as color retention, mar-resistance, chalk-resistance, dirt-resistance, etc. Thus, primer coatings can be formulated with major emphasis on adhesion to substrates, and adhesion to subsequent basecoats and/or topcoats.
In many applications, it is desirable that the primer coating be electroconductive to allow the application of base coats or top coats over these primers by electrostatic coating techniques. Conductive materials, particularly conductive powders such as carbon blacks and various inorganic additives have been included in the coating compositions to impart the desired conductive characteristics to the coating. Satisfactory conductivity levels are obtained but the inorganic conductive additives are often rejected because of excessive weight and/or objectionable color. Poor tolerance of humidity variations is often a characteristic of such additives.
Dialkyl diallyl ammonium salts such as the chloride salts, and homopolymer and copolymers of said salts have been suggested as useful components in coatings for preparing electroconductive paper. U.S. Pat. No. 4,222,901 describes electroconductive resin coating compositions containing a copolymer of a quaternary ammonium conductive monomer and at least 15% by weight of acrylamide. Various conductive polymers are described including polymers derived from dialkyl diallyl ammonium chloride. Other patents describing the use of dialkyl diallyl ammonium salts, polymers and copolymers thereof, and mixtures with other materials in conductive coatings for paper include, for example, U.S. Pat. No. 4,084,034 which describes and claims electroconductive paper having a layer containing sodium chloride in a water-soluble polymer consisting of units derived from dimethyl diallyl ammonium chloride. The electroconductive paper can be used to distribute electrical stresses in various insulating products and in various types of non-impact printing processes such as electrostatographic, electrophotographic, electrographic, etc. U.S. Pat. No. Re. 28,543 discloses a variety of electroconductive materials including polymers of diallyl ammonium chloride for use in non-impact printing. Copolymers also are disclosed.
The literature also includes suggestions of the use of resin compositions containing dialkyl diallyl ammonium polymers and copolymers as textile-treating agents, as core binders, and adhesive and laminating compositions, as thickening agents, etc.
The preparation of and the description of various dialkyl diallyl ammonium salts, polymers and copolymers also is contained in various patents and publications including U.S. Pat. Nos. 2,923,701; 3,461,163; 3,674,711; 4,222,901; and Re 28,543.
U.S. Pat. No. 3,674,711 also describes clear transparent conductive films by combining a quaternary ammonium polyelectrolyte, such as polydimethyl diallyl ammonium chloride, with a film-forming polymer such as polyvinyl alcohol and a neutral solvent such as water. The mixture can be cast on a smooth surface (e.g., glass), the mutual solvent evaporated, and the resultant sheet material stripped from the casting surface to obtain a sheet of electrically conductive clear transparent plastic material useful as a conductive plastic or, after coating with a charge retentive film, as an electrographic recording medium.
For many years, curable coating compositions useful as paints, varnishes, etc., have been dissolved in volatile hydrocarbon solvents to facilitate the deposition of thin films on the substrates to be coated and to enable the solvent to evaporate into the atmosphere within a reasonable period of time leaving a dry nontacky coating. The use of such volatile hydrocarbon solvents as diluents, therefore, results in air pollution problems.
More recently, the coatings industry has directed its attention to the problem of volatile organic emissions from organic coating compositions. These efforts have been encouraged by various governmental and state agencies concerned with the air pollution caused by the use of volatile hydrocarbon solvents. Such efforts by the coatings industry has resulted in the development of a number of high-solids resin or water-borne coating formulations which contain significantly reduced amounts of solvents, and, in some instances, little or no solvent.
Some difficulty has been observed in coating certain substrates with these high solids, low solvent coating compositions necessitating the use of primer coatings which generally contain very high levels of solvents.